An introduction to A/B testing and optimization
A comprehensive guide to A/B testing, explaining the differences between A/B and multivariate testing, how to conduct tests in a structured and progressive way, and the thought process behind choosing the right experiment.
Summarize this articleHere’s what you need to know:
- A/B testing is a scientific method for comparing two versions of a webpage or app to see which performs better for a specific goal, like increasing conversions or user engagement.
- It’s a powerful tool for optimizing websites, mobile apps, emails, and more, and can help solve UX issues, improve performance, and boost engagement.
- To run an A/B test, you first define a problem or user behavior you want to address. Then, you create variations of your original element and split website traffic between them. Finally, you collect and analyze data to see which variation performs best.
- Common A/B tests include testing different navigation menus, optimizing landing pages, and experimenting with promotional messages.
A/B testing is a method of comparing two versions of a webpage or app against each other to determine which one performs better against a specific objective. It is one of the most widely used techniques for maximizing the performance of digital assets such as websites, mobile applications, SaaS products, emails, and more.
Controlled experiments provide marketers, product managers, and engineers with the agility to iterate fast and at scale, leading to data-driven, thoroughly informed decisions about their creative ideas. With A/B tests, you can stop wondering why some things are not working, because the proof is in the pudding. It’s the perfect method to improve conversion rate, increase revenue, grow your subscribers base, and improve your customer acquisition and lead generation results.
Some of the most innovative companies, like Google, Amazon, Netflix, and Facebook, developed lean business approaches, allowing them to run over thousands of experiments each year.
As Jeff Bezos has once said: “Our success at Amazon is a function of how many experiments we do per year, per month, per week, per day.”
Netflix wrote in one of their technology blogs back in April 2016: “By following an empirical approach, we ensure that product changes are not driven by the most opinionated and vocal Netflix employees, but instead by actual data, allowing our members themselves to guide us toward the experiences they love.”
And Mark Zuckerberg once explained that one of the things he is mostly proud of that is really key to their success is their testing framework: “At any given point in time, there isn’t just one version of Facebook running. There are probably 10,000.”
What is an A/B Test?
In a classic A/B testing procedure, we decide what we would like to test and what our objective is. Then, we create one or more variations of our original web element (a.k.a. the control group, or the baseline). Next, we split the website traffic randomly between two variations (i.e., we randomly allocate visitors according to some probability), and finally, we collect data regarding our web page performance (metrics). After some time, we look at the data, pick the variation that performed best, and cancel the one that performed poorly.
If not done correctly, tests can fail to produce meaningful, valuable results and can even mislead. Generally speaking, running controlled experiments can help organizations with:
- Solving UX issues and common visitor pain points
- Improving performance from existing traffic (higher conversions and revenue, improve customer acquisition costs)
- Increasing overall engagement (reducing bounce rate, improving click-through rate, and more.)
We must keep in mind that the moment we pick a variation, we are generalizing the measures we collected up to that point to the entire population of potential visitors. This is a significant leap of faith, and it must be done in a valid way. Otherwise, we are eventually bound to make a bad decision that will harm the web page in the long run. The process of gaining validity is called hypothesis testing, and the validity we seek is called statistical significance.
Some examples of A/B tests:
- Testing different sorting orders of the site’s navigation menu (Like in this example from a large electronics retailer in Germany)
- Testing and optimizing landing pages (Like in this example from a European leading airline passenger protection company)
- Testing promotional messages, like newsletter subscription overlays and banners (Like in this example from an international boutique retailer of natural bath products)
How an A/B test is born: Constructing a hypothesis
An A/B test starts by identifying a problem that you wish to resolve, or a user behavior you want to encourage or influence. Once identified, the marketer would typically conclude a hypothesis – an educated guess that will either validate or invalidate the experiment’s results.
Example hypothesis: Adding a Social Proof badge to your Product Detail Pages (PDP) will inform visitors of the product’s popularity and increase add-to-cart events by 10%.
In this case, once the problem is identified (low add-to-cart rate, as an example) and a hypothesis is worked out (adding a social proof badge to encourage more website visitors to add items to their carts), you are ready to test it on your site.
The classic approach to A/B testing
In a simple A/B test, traffic is split between two variations of content. One is considered the control and contains the original content and design. The other functions as a new version of the controlled variation. The variation may be different in many aspects. For example, we could test a variation with different headline text, call-to-action buttons, a new layout or design, and so on.
In a classic page-level experiment, you don’t necessarily need two different URLs to run a proper test. Most A/B testing solutions will let you create variations dynamically by modifying the content, layout, or design of the page.
However, if you have two (or more) sets of pages that you’re looking to include in a controlled test, you should probably consider using a split URL test.
When to use split URL tests
Split URL testing, sometimes referred to as “multi-page” or “multi-URL” testing, is a similar method to a standard A/B test, which allows you to conduct experiments based on separate URLs of each variation.
With this method, you can conduct tests between two existing URLs, which is especially useful when serving dynamic content. Run a split URL test when you already have two existing pages and want to test which one of them performs better.
For example, if you’re running a campaign and you have two different versions for potential landing pages, you can run a split URL test to examine which one will perform better for that particular campaign.
An A/B test is not limited to just two variations
If you want to test more than just two variations, you can run an A/B/n test. A/B/n tests allow you to measure the performance of three or more variations instead of testing only one variation against a control page. High-traffic sites can use this testing method to evaluate the performance of a much broader set of changes and maximize test time with faster results.
However, although it is useful for any testing, from minor to dramatic changes, I recommend not making too many changes between the control and variation. Try making just a few critical and prominent changes to understand the possible causal reasons for the results of the experiment. If you are looking to test changes to multiple elements on a web page, consider running a multivariate test.
What are Multivariate tests?
Multivariate tests, sometimes referred to as “multi-variant” tests, allow you to test changes to multiple sections on a single page. As an example, run a multivariate test on one of your landing pages and change it with two new elements. In the first version, add a contact form instead of the main image. In the second version, add a video item. The system will now generate another possible combination based on your changes, which includes both the video and the contact form:
Total test versions: 2 x 2 = 4
V1 – Control variation (no contact form and no video item)
V2 – Contact form version
V3 – Video item version
V4 – Contact form + video item version
Since multivariate tests generate all possible combinations of your changes, it is not recommended to create a large number of variations unless you’re running the test on a high-traffic site. On the other hand, running multivariate tests on low-traffic sites will provide poor results and insufficient data to draw any significant conclusions. Be sure to have at least a few thousand monthly visitors to your site before choosing to run a multivariate test.

Example of a multivariate test on an eCommerce product-listing page
When to use each test type
A/B tests will help you answer questions such as: which of the two versions of my page perform better in terms of the visitor’s response to it?
Multivariate tests will answer questions like:
- Do visitors respond better to a video item next to a contact form?
- Or to a webpage with just a contact form and no video item?
- Or to a webpage with a video item but no contact form?
How to measure the effectiveness of the A/B testing platform
One method of determining the effectiveness of an A/B testing platform is to perform an A/A test. This means that you create two or more identical variations and run an A/B test to see how the platform handles the variations. Successful results should show that both variations yield very similar results. You can read further about A/A tests here.
The road to A/B test success
“I didn’t fail the test, I just found 100 ways to do it wrong.” / Benjamin Franklin
When running an A/B test, using a valid methodology is crucial for our ability to rely on the test results to produce better performance long after the test is over. In other words, we try to understand if tested changes directly affect visitor behavior or occur due to random chance. A/B testing provides a framework that allows us to measure the difference in visitor response between variations and, if detected, establishes statistical significance, and to some extent causation.
Questions and answers
When designing an A/B test, it’s crucial to define clear objectives and select the right metrics that align with these goals. Randomization is essential to avoid bias, and calculating the appropriate sample size ensures statistical significance. The test should run for an adequate duration to capture variations in user behavior over time. Additionally, controlling for external factors, such as marketing campaigns or seasonal trends, helps in obtaining reliable results. By addressing these considerations, businesses can ensure that their A/B tests provide meaningful and actionable insights.
Interpreting A/B test results involves statistical analysis to determine significance and calculating confidence intervals to understand the range of the true effect size. It’s important to consider the broader context, including user behavior patterns and external influences. Segmentation analysis can reveal variations in performance across different user groups. The insights gained should be translated into actionable strategies, and iterative testing should be used to refine hypotheses and optimize outcomes continuously. This approach ensures that businesses make informed, data-driven decisions.
Advanced A/B testing techniques include multi-armed bandit testing, which dynamically allocates traffic to better-performing variations, and sequential testing, which allows for continuous monitoring and early stopping of tests. Bayesian methods provide a flexible approach to decision-making by updating outcome probabilities as data is collected. Personalization tailors variations to different user segments, and integrating machine learning algorithms can predict outcomes and optimize test designs. These techniques enhance the accuracy and depth of insights, leading to more effective optimization strategies.
Integrating A/B testing into a digital marketing strategy involves aligning testing initiatives with business objectives and fostering cross-functional collaboration between marketing, product, and analytics teams. Data from A/B tests should be integrated with other marketing analytics to provide a comprehensive view of performance. A/B testing should be used as a tool for continuous improvement, regularly testing and optimizing various aspects of the digital experience. Developing a scalable testing framework allows for efficient execution and analysis of multiple tests, ensuring that insights are actionable and impactful.
Ethical considerations in A/B testing include ensuring user consent, especially when personal data is involved, and protecting user data in compliance with regulations like GDPR or CCPA. Transparency about the purpose of the tests and how data will be used is crucial. Tests should be designed to avoid causing harm or negative experiences for users, and fairness should be maintained to ensure no particular group of users is disadvantaged. By addressing these ethical considerations, businesses can conduct A/B tests responsibly and maintain user trust.
Hypothesis formulation is a critical step in the A/B testing process as it provides a clear direction and purpose for the test. A well-defined hypothesis outlines the expected outcome and the rationale behind the changes being tested. This helps in setting measurable goals and ensures that the test is focused on addressing specific issues or opportunities. A strong hypothesis also aids in interpreting the results and making informed decisions based on the findings.
While A/B testing is a powerful tool, it has limitations such as the potential for inconclusive results if the sample size is too small or the test duration is too short. Additionally, A/B testing may not account for long-term user behavior changes or external factors influencing results. To address these limitations, it’s important to ensure adequate sample sizes and test durations, complement A/B testing with other research methods, and continuously monitor and iterate on the findings to adapt to changing conditions.
To ensure scalability and sustainability in A/B testing practices, businesses should invest in robust testing platforms that automate the process and provide comprehensive analytics. Developing a structured testing framework with clear guidelines and best practices helps in maintaining consistency and efficiency. Training teams on the importance of A/B testing and fostering a culture of experimentation encourages continuous improvement. Regularly reviewing and updating testing strategies based on learnings and technological advancements ensures that the practices remain relevant and effective.